Thanks for your response. We changed the file content as per your link under Common-database.nmis, however It didnt make any difference. Its been over 2 weeks since we changed the values but if I export a report which is over 8 days it's compressing to 30 min. rather than expected 5 min intervals.

Do we have to change any thing else or restart a service!

That's how our Interface section looks like under /usr/local/nmis8/models/Common-database.nmis